I think the biggest problem with the CUES groupset, is that they made the derailleur pull ratio different than their well established 10-11 speed road groupsets, or their 10-11 MTB groupsets. It's just mind boggling why they would introduce a third set of pull ratios totally incompatible with the two existing road or MTB universes.
The thinking behind using the same 11 speed cog spacing to create 9 and 10 speed variants, was totally valid. It was just hobbled by the derailleur pull ratios.